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Different Stellar Rotations in the Two Main Sequences of the Young Globular Cluster NGC 1818: The First Direct Spectroscopic Evidence

Marino, Anna Fabiola; Przybilla, N; Milone, Antonino P; Da Costa, Gary; D'Antona, Francesca; Dotter, Aaron; Dupree, A. K.

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We present a spectroscopic analysis of main sequence (MS) stars in the young globular cluster NGC1818 (age~40 Myrs) in the Large Magellanic Cloud. Our photometric survey on Magellanic Clouds clusters has revealed that NGC1818, similarly to the other young objects with age 600 Myrs, displays not only an extended MS Turn-Off (eMSTO), as observed in intermediate-age clusters (age~1-2 Gyrs), but also a split MS. The most straightforward interpretation of the double MS is the presence of two stellar...[Show more]

dc.contributor.authorMarino, Anna Fabiola
dc.contributor.authorPrzybilla, N
dc.contributor.authorMilone, Antonino P
dc.contributor.authorDa Costa, Gary
dc.contributor.authorD'Antona, Francesca
dc.contributor.authorDotter, Aaron
dc.contributor.authorDupree, A. K.
dc.date.accessioned2020-01-10T04:33:26Z
dc.date.available2020-01-10T04:33:26Z
dc.identifier.issn0004-6256
dc.identifier.urihttp://hdl.handle.net/1885/196909
dc.description.abstractWe present a spectroscopic analysis of main sequence (MS) stars in the young globular cluster NGC1818 (age~40 Myrs) in the Large Magellanic Cloud. Our photometric survey on Magellanic Clouds clusters has revealed that NGC1818, similarly to the other young objects with age 600 Myrs, displays not only an extended MS Turn-Off (eMSTO), as observed in intermediate-age clusters (age~1-2 Gyrs), but also a split MS. The most straightforward interpretation of the double MS is the presence of two stellar populations: a sequence of slowly-rotating stars lying on the blue-MS and a sequence of fast rotators, with rotation close to the breaking speed, defining a red-MS. We report the first direct spectroscopic measurements of projected rotational velocities vsini for the double MS, eMSTO and Be stars of a young cluster. The analysis of line profiles includes non-LTE effects, required for correctly deriving v sini values. Our results suggest that: (i) the mean rotation for blue- and red-MS stars is vsini=71\pm10 km/s (sigma=37 km/s) and vsini=202\pm23 km/s (sigma=91 km/s), respectively; (ii) eMSTO stars have different vsini, which are generally lower than those inferred for red-MS stars, and (iii) as expected, Be stars display the highest vsini values. This analyis supports the idea that distinct rotational velocities play an important role in the appearence of multiple stellar populations in the color-magnitude diagrams of young clusters, and poses new constraints to the current scenarios.
dc.description.sponsorshipThe authors are grateful to the anonymous referee for useful discussions. A.F.M. and G.D.C. acknowledge support by the Australian Research Council through Discovery Early Career Researcher Award DE160100851 and Discovery project DP150103294. A.P.M. has been supported by the European Research Council through the Starting Grant “GALFOR” and the FARE-MIUR project R164RM93XW “SEMPLICE.”
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherAmerican Astronomical Society
dc.rights© 2018. The American Astronomical Society
dc.sourceAstronomical Journal
dc.titleDifferent Stellar Rotations in the Two Main Sequences of the Young Globular Cluster NGC 1818: The First Direct Spectroscopic Evidence
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume156
dc.date.issued2018
local.identifier.absfor020103 - Cosmology and Extragalactic Astronomy
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationu4485658xPUB124
local.publisher.urlhttps://aas.org/
local.type.statusPublished Version
local.contributor.affiliationMarino, Anna, College of Science, ANU
local.contributor.affiliationPrzybilla, N, University of Innsbruck
local.contributor.affiliationMilone, Antonino P, Università di Padova
local.contributor.affiliationDa Costa, Gary, College of Science, ANU
local.contributor.affiliationD'Antona, Francesca, INAF-Osservatorio Astronomico di Roma
local.contributor.affiliationDotter, Aaron, Harvard-Smithsonian Center for Astrophysics
local.contributor.affiliationDupree, A. K., Harvard-Smithsonian Center for Astrophysics
dc.relationhttp://purl.org/au-research/grants/arc/DE160100851
dc.relationhttp://purl.org/au-research/grants/arc/DP150103294
local.bibliographicCitation.issue116
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage10
local.identifier.doi10.3847/1538-3881/aad3cd
local.identifier.absseo970102 - Expanding Knowledge in the Physical Sciences
dc.date.updated2019-08-25T08:19:41Z
local.identifier.scopusID2-s2.0-85053144774
dcterms.accessRightsOpen Access
dc.provenancehttp://sherpa.ac.uk/romeo/issn/0004-6256/..."author can archive publisher's version/PDF" from Sherpa/Romeo site (as at 10 Jan 2020)
CollectionsANU Research Publications

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